2 files changed, 13 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
index 2cdc8af688..ae59176fa3 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
@@ -248,7 +248,8 @@ module ActiveRecord
       if spec.kind_of?(ActiveRecord::ConnectionAdapters::AbstractAdapter)
         active_connections[name] = spec
       elsif spec.kind_of?(ConnectionSpecification)
-        self.connection = self.send(spec.adapter_method, spec.config)
+        config = spec.config.reverse_merge(:allow_concurrency => @@allow_concurrency)
+        self.connection = self.send(spec.adapter_method, config)
       elsif spec.nil?
         raise ConnectionNotEstablished
       else
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index c45454eacc..d91b919116 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -91,6 +91,17 @@ module ActiveRecord
         end
       end
 
+      # Appends a locking clause to a SQL statement. *Modifies the +sql+ parameter*.
+      #   # SELECT * FROM suppliers FOR UPDATE
+      #   add_lock! 'SELECT * FROM suppliers', :lock => true
+      #   add_lock! 'SELECT * FROM suppliers', :lock => ' FOR UPDATE'
+      def add_lock!(sql, options)
+        case lock = options[:lock]
+          when true:   sql << ' FOR UPDATE'
+          when String: sql << " #{lock}"
+        end
+      end
+
       def default_sequence_name(table, column)
         nil
       end